// SPDX-License-Identifier: GPL-2.0-only
/*
 * Based on arch/arm/kernel/signal.c
 *
 * Copyright (C) 1995-2009 Russell King
 * Copyright (C) 2012 ARM Ltd.
 */

#include <linux/cache.h>
#include <linux/compat.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/personality.h>
#include <linux/freezer.h>
#include <linux/stddef.h>
#include <linux/uaccess.h>
#include <linux/sizes.h>
#include <linux/string.h>
#include <linux/tracehook.h>
#include <linux/ratelimit.h>
#include <linux/syscalls.h>

#include <asm/daifflags.h>
#include <asm/debug-monitors.h>
#include <asm/elf.h>
#include <asm/cacheflush.h>
#include <asm/ucontext.h>
#include <asm/unistd.h>
#include <asm/fpsimd.h>
#include <asm/ptrace.h>
#include <asm/signal32.h>
#include <asm/traps.h>
#include <asm/vdso.h>

/*
 * Do a signal return; undo the signal stack. These are aligned to 128-bit.
 */
struct rt_sigframe {
        struct siginfo info;
        struct ucontext uc;
};

struct frame_record {
        u64 fp;
        u64 lr;
};

struct rt_sigframe_user_layout {
        struct rt_sigframe __user *sigframe;
        struct frame_record __user *next_frame;

        unsigned long size;     /* size of allocated sigframe data */
        unsigned long limit;    /* largest allowed size */

        unsigned long fpsimd_offset;
        unsigned long esr_offset;
        unsigned long sve_offset;
        unsigned long extra_offset;
        unsigned long end_offset;
};

#define BASE_SIGFRAME_SIZE round_up(sizeof(struct rt_sigframe), 16)
#define TERMINATOR_SIZE round_up(sizeof(struct _aarch64_ctx), 16)
#define EXTRA_CONTEXT_SIZE round_up(sizeof(struct extra_context), 16)

static void init_user_layout(struct rt_sigframe_user_layout *user)
{
        const size_t reserved_size =
                sizeof(user->sigframe->uc.uc_mcontext.__reserved);

        memset(user, 0, sizeof(*user));
        user->size = offsetof(struct rt_sigframe, uc.uc_mcontext.__reserved);

        user->limit = user->size + reserved_size;

        user->limit -= TERMINATOR_SIZE;
        user->limit -= EXTRA_CONTEXT_SIZE;
        /* Reserve space for extension and terminator ^ */
}

static size_t sigframe_size(struct rt_sigframe_user_layout const *user)
{
        return round_up(max(user->size, sizeof(struct rt_sigframe)), 16);
}

/*
 * Sanity limit on the approximate maximum size of signal frame we'll
 * try to generate.  Stack alignment padding and the frame record are
 * not taken into account.  This limit is not a guarantee and is
 * NOT ABI.
 */
#define SIGFRAME_MAXSZ SZ_64K

static int __sigframe_alloc(struct rt_sigframe_user_layout *user,
                            unsigned long *offset, size_t size, bool extend)
{
        size_t padded_size = round_up(size, 16);

        if (padded_size > user->limit - user->size &&
            !user->extra_offset &&
            extend) {
                int ret;

                user->limit += EXTRA_CONTEXT_SIZE;
                ret = __sigframe_alloc(user, &user->extra_offset,
                                       sizeof(struct extra_context), false);
                if (ret) {
                        user->limit -= EXTRA_CONTEXT_SIZE;
                        return ret;
                }

                /* Reserve space for the __reserved[] terminator */
                user->size += TERMINATOR_SIZE;

                /*
                 * Allow expansion up to SIGFRAME_MAXSZ, ensuring space for
                 * the terminator:
                 */
                user->limit = SIGFRAME_MAXSZ - TERMINATOR_SIZE;
        }

        /* Still not enough space?  Bad luck! */
        if (padded_size > user->limit - user->size)
                return -ENOMEM;

        *offset = user->size;
        user->size += padded_size;

        return 0;
}

/*
 * Allocate space for an optional record of <size> bytes in the user
 * signal frame.  The offset from the signal frame base address to the
 * allocated block is assigned to *offset.
 */
static int sigframe_alloc(struct rt_sigframe_user_layout *user,
                          unsigned long *offset, size_t size)
{
        return __sigframe_alloc(user, offset, size, true);
}

/* Allocate the null terminator record and prevent further allocations */
static int sigframe_alloc_end(struct rt_sigframe_user_layout *user)
{
        int ret;

        /* Un-reserve the space reserved for the terminator: */
        user->limit += TERMINATOR_SIZE;

        ret = sigframe_alloc(user, &user->end_offset,
                             sizeof(struct _aarch64_ctx));
        if (ret)
                return ret;

        /* Prevent further allocation: */
        user->limit = user->size;
        return 0;
}

static void __user *apply_user_offset(
        struct rt_sigframe_user_layout const *user, unsigned long offset)
{
        char __user *base = (char __user *)user->sigframe;

        return base + offset;
}

static int preserve_fpsimd_context(struct fpsimd_context __user *ctx)
{
        struct user_fpsimd_state const *fpsimd =
                &current->thread.uw.fpsimd_state;
        int err;

        /* copy the FP and status/control registers */
        err = __copy_to_user(ctx->vregs, fpsimd->vregs, sizeof(fpsimd->vregs));
        __put_user_error(fpsimd->fpsr, &ctx->fpsr, err);
        __put_user_error(fpsimd->fpcr, &ctx->fpcr, err);

        /* copy the magic/size information */
        __put_user_error(FPSIMD_MAGIC, &ctx->head.magic, err);
        __put_user_error(sizeof(struct fpsimd_context), &ctx->head.size, err);

        return err ? -EFAULT : 0;
}

static int restore_fpsimd_context(struct fpsimd_context __user *ctx)
{
        struct user_fpsimd_state fpsimd;
        __u32 magic, size;
        int err = 0;

        /* check the magic/size information */
        __get_user_error(magic, &ctx->head.magic, err);
        __get_user_error(size, &ctx->head.size, err);
        if (err)
                return -EFAULT;
        if (magic != FPSIMD_MAGIC || size != sizeof(struct fpsimd_context))
                return -EINVAL;

        /* copy the FP and status/control registers */
        err = __copy_from_user(fpsimd.vregs, ctx->vregs,
                               sizeof(fpsimd.vregs));
        __get_user_error(fpsimd.fpsr, &ctx->fpsr, err);
        __get_user_error(fpsimd.fpcr, &ctx->fpcr, err);

        clear_thread_flag(TIF_SVE);

        /* load the hardware registers from the fpsimd_state structure */
        if (!err)
                fpsimd_update_current_state(&fpsimd);

        return err ? -EFAULT : 0;
}


struct user_ctxs {
        struct fpsimd_context __user *fpsimd;
        struct sve_context __user *sve;
};

#ifdef CONFIG_ARM64_SVE

static int preserve_sve_context(struct sve_context __user *ctx)
{
        int err = 0;
        u16 reserved[ARRAY_SIZE(ctx->__reserved)];
        unsigned int vl = current->thread.sve_vl;
        unsigned int vq = 0;

        if (test_thread_flag(TIF_SVE))
                vq = sve_vq_from_vl(vl);

        memset(reserved, 0, sizeof(reserved));

        __put_user_error(SVE_MAGIC, &ctx->head.magic, err);
        __put_user_error(round_up(SVE_SIG_CONTEXT_SIZE(vq), 16),
                         &ctx->head.size, err);
        __put_user_error(vl, &ctx->vl, err);
        BUILD_BUG_ON(sizeof(ctx->__reserved) != sizeof(reserved));
        err |= __copy_to_user(&ctx->__reserved, reserved, sizeof(reserved));

        if (vq) {
                /*
                 * This assumes that the SVE state has already been saved to
                 * the task struct by calling preserve_fpsimd_context().
                 */
                err |= __copy_to_user((char __user *)ctx + SVE_SIG_REGS_OFFSET,
                                      current->thread.sve_state,
                                      SVE_SIG_REGS_SIZE(vq));
        }

        return err ? -EFAULT : 0;
}

static int restore_sve_fpsimd_context(struct user_ctxs *user)
{
        int err;
        unsigned int vq;
        struct user_fpsimd_state fpsimd;
        struct sve_context sve;

        if (__copy_from_user(&sve, user->sve, sizeof(sve)))
                return -EFAULT;

        if (sve.vl != current->thread.sve_vl)
                return -EINVAL;

        if (sve.head.size <= sizeof(*user->sve)) {
                clear_thread_flag(TIF_SVE);
                goto fpsimd_only;
        }

        vq = sve_vq_from_vl(sve.vl);

        if (sve.head.size < SVE_SIG_CONTEXT_SIZE(vq))
                return -EINVAL;

        /*
         * Careful: we are about __copy_from_user() directly into
         * thread.sve_state with preemption enabled, so protection is
         * needed to prevent a racing context switch from writing stale
         * registers back over the new data.
         */

        fpsimd_flush_task_state(current);
        /* From now, fpsimd_thread_switch() won't touch thread.sve_state */

        sve_alloc(current);
        err = __copy_from_user(current->thread.sve_state,
                               (char __user const *)user->sve +
                                        SVE_SIG_REGS_OFFSET,
                               SVE_SIG_REGS_SIZE(vq));
        if (err)
                return -EFAULT;

        set_thread_flag(TIF_SVE);

fpsimd_only:
        /* copy the FP and status/control registers */
        /* restore_sigframe() already checked that user->fpsimd != NULL. */
        err = __copy_from_user(fpsimd.vregs, user->fpsimd->vregs,
                               sizeof(fpsimd.vregs));
        __get_user_error(fpsimd.fpsr, &user->fpsimd->fpsr, err);
        __get_user_error(fpsimd.fpcr, &user->fpsimd->fpcr, err);

        /* load the hardware registers from the fpsimd_state structure */
        if (!err)
                fpsimd_update_current_state(&fpsimd);

        return err ? -EFAULT : 0;
}

#else /* ! CONFIG_ARM64_SVE */

/* Turn any non-optimised out attempts to use these into a link error: */
extern int preserve_sve_context(void __user *ctx);
extern int restore_sve_fpsimd_context(struct user_ctxs *user);

#endif /* ! CONFIG_ARM64_SVE */


static int parse_user_sigframe(struct user_ctxs *user,
                               struct rt_sigframe __user *sf)
{
        struct sigcontext __user *const sc = &sf->uc.uc_mcontext;
        struct _aarch64_ctx __user *head;
        char __user *base = (char __user *)&sc->__reserved;
        size_t offset = 0;
        size_t limit = sizeof(sc->__reserved);
        bool have_extra_context = false;
        char const __user *const sfp = (char const __user *)sf;

        user->fpsimd = NULL;
        user->sve = NULL;

        if (!IS_ALIGNED((unsigned long)base, 16))
                goto invalid;

        while (1) {
                int err = 0;
                u32 magic, size;
                char const __user *userp;
                struct extra_context const __user *extra;
                u64 extra_datap;
                u32 extra_size;
                struct _aarch64_ctx const __user *end;
                u32 end_magic, end_size;

                if (limit - offset < sizeof(*head))
                        goto invalid;

                if (!IS_ALIGNED(offset, 16))
                        goto invalid;

                head = (struct _aarch64_ctx __user *)(base + offset);
                __get_user_error(magic, &head->magic, err);
                __get_user_error(size, &head->size, err);
                if (err)
                        return err;

                if (limit - offset < size)
                        goto invalid;

                switch (magic) {
                case 0:
                        if (size)
                                goto invalid;

                        goto done;

                case FPSIMD_MAGIC:
                        if (!system_supports_fpsimd())
                                goto invalid;
                        if (user->fpsimd)
                                goto invalid;

                        if (size < sizeof(*user->fpsimd))
                                goto invalid;

                        user->fpsimd = (struct fpsimd_context __user *)head;
                        break;

                case ESR_MAGIC:
                        /* ignore */
                        break;

                case SVE_MAGIC:
                        if (!system_supports_sve())
                                goto invalid;

                        if (user->sve)
                                goto invalid;

                        if (size < sizeof(*user->sve))
                                goto invalid;

                        user->sve = (struct sve_context __user *)head;
                        break;

                case EXTRA_MAGIC:
                        if (have_extra_context)
                                goto invalid;

                        if (size < sizeof(*extra))
                                goto invalid;

                        userp = (char const __user *)head;

                        extra = (struct extra_context const __user *)userp;
                        userp += size;

                        __get_user_error(extra_datap, &extra->datap, err);
                        __get_user_error(extra_size, &extra->size, err);
                        if (err)
                                return err;

                        /* Check for the dummy terminator in __reserved[]: */

                        if (limit - offset - size < TERMINATOR_SIZE)
                                goto invalid;

                        end = (struct _aarch64_ctx const __user *)userp;
                        userp += TERMINATOR_SIZE;

                        __get_user_error(end_magic, &end->magic, err);
                        __get_user_error(end_size, &end->size, err);
                        if (err)
                                return err;

                        if (end_magic || end_size)
                                goto invalid;

                        /* Prevent looping/repeated parsing of extra_context */
                        have_extra_context = true;

                        base = (__force void __user *)extra_datap;
                        if (!IS_ALIGNED((unsigned long)base, 16))
                                goto invalid;

                        if (!IS_ALIGNED(extra_size, 16))
                                goto invalid;

                        if (base != userp)
                                goto invalid;

                        /* Reject "unreasonably large" frames: */
                        if (extra_size > sfp + SIGFRAME_MAXSZ - userp)
                                goto invalid;

                        /*
                         * Ignore trailing terminator in __reserved[]
                         * and start parsing extra data:
                         */
                        offset = 0;
                        limit = extra_size;

                        if (!access_ok(base, limit))
                                goto invalid;

                        continue;

                default:
                        goto invalid;
                }

                if (size < sizeof(*head))
                        goto invalid;

                if (limit - offset < size)
                        goto invalid;

                offset += size;
        }

done:
        return 0;

invalid:
        return -EINVAL;
}

static int restore_sigframe(struct pt_regs *regs,
                            struct rt_sigframe __user *sf)
{
        sigset_t set;
        int i, err;
        struct user_ctxs user;

        err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
        if (err == 0)
                set_current_blocked(&set);

        for (i = 0; i < 31; i++)
                __get_user_error(regs->regs[i], &sf->uc.uc_mcontext.regs[i],
                                 err);
        __get_user_error(regs->sp, &sf->uc.uc_mcontext.sp, err);
        __get_user_error(regs->pc, &sf->uc.uc_mcontext.pc, err);
        __get_user_error(regs->pstate, &sf->uc.uc_mcontext.pstate, err);

        /*
         * Avoid sys_rt_sigreturn() restarting.
         */
        forget_syscall(regs);

        err |= !valid_user_regs(&regs->user_regs, current);
        if (err == 0)
                err = parse_user_sigframe(&user, sf);

        if (err == 0 && system_supports_fpsimd()) {
                if (!user.fpsimd)
                        return -EINVAL;

                if (user.sve) {
                        if (!system_supports_sve())
                                return -EINVAL;

                        err = restore_sve_fpsimd_context(&user);
                } else {
                        err = restore_fpsimd_context(user.fpsimd);
                }
        }

        return err;
}

SYSCALL_DEFINE0(rt_sigreturn)
{
        struct pt_regs *regs = current_pt_regs();
        struct rt_sigframe __user *frame;

        /* Always make any pending restarted system calls return -EINTR */
        current->restart_block.fn = do_no_restart_syscall;

        /*
         * Since we stacked the signal on a 128-bit boundary, then 'sp' should
         * be word aligned here.
         */
        if (regs->sp & 15)
                goto badframe;

        frame = (struct rt_sigframe __user *)regs->sp;

        if (!access_ok(frame, sizeof (*frame)))
                goto badframe;

        if (restore_sigframe(regs, frame))
                goto badframe;

        if (restore_altstack(&frame->uc.uc_stack))
                goto badframe;

        return regs->regs[0];

badframe:
        arm64_notify_segfault(regs->sp);
        return 0;
}

/*
 * Determine the layout of optional records in the signal frame
 *
 * add_all: if true, lays out the biggest possible signal frame for
 *      this task; otherwise, generates a layout for the current state
 *      of the task.
 */
static int setup_sigframe_layout(struct rt_sigframe_user_layout *user,
                                 bool add_all)
{
        int err;

        err = sigframe_alloc(user, &user->fpsimd_offset,
                             sizeof(struct fpsimd_context));
        if (err)
                return err;

        /* fault information, if valid */
        if (add_all || current->thread.fault_code) {
                err = sigframe_alloc(user, &user->esr_offset,
                                     sizeof(struct esr_context));
                if (err)
                        return err;
        }

        if (system_supports_sve()) {
                unsigned int vq = 0;

                if (add_all || test_thread_flag(TIF_SVE)) {
                        int vl = sve_max_vl;

                        if (!add_all)
                                vl = current->thread.sve_vl;

                        vq = sve_vq_from_vl(vl);
                }

                err = sigframe_alloc(user, &user->sve_offset,
                                     SVE_SIG_CONTEXT_SIZE(vq));
                if (err)
                        return err;
        }

        return sigframe_alloc_end(user);
}

static int setup_sigframe(struct rt_sigframe_user_layout *user,
                          struct pt_regs *regs, sigset_t *set)
{
        int i, err = 0;
        struct rt_sigframe __user *sf = user->sigframe;

        /* set up the stack frame for unwinding */
        __put_user_error(regs->regs[29], &user->next_frame->fp, err);
        __put_user_error(regs->regs[30], &user->next_frame->lr, err);

        for (i = 0; i < 31; i++)
                __put_user_error(regs->regs[i], &sf->uc.uc_mcontext.regs[i],
                                 err);
        __put_user_error(regs->sp, &sf->uc.uc_mcontext.sp, err);
        __put_user_error(regs->pc, &sf->uc.uc_mcontext.pc, err);
        __put_user_error(regs->pstate, &sf->uc.uc_mcontext.pstate, err);

        __put_user_error(current->thread.fault_address, &sf->uc.uc_mcontext.fault_address, err);

        err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(*set));

        if (err == 0 && system_supports_fpsimd()) {
                struct fpsimd_context __user *fpsimd_ctx =
                        apply_user_offset(user, user->fpsimd_offset);
                err |= preserve_fpsimd_context(fpsimd_ctx);
        }

        /* fault information, if valid */
        if (err == 0 && user->esr_offset) {
                struct esr_context __user *esr_ctx =
                        apply_user_offset(user, user->esr_offset);

                __put_user_error(ESR_MAGIC, &esr_ctx->head.magic, err);
                __put_user_error(sizeof(*esr_ctx), &esr_ctx->head.size, err);
                __put_user_error(current->thread.fault_code, &esr_ctx->esr, err);
        }

        /* Scalable Vector Extension state, if present */
        if (system_supports_sve() && err == 0 && user->sve_offset) {
                struct sve_context __user *sve_ctx =
                        apply_user_offset(user, user->sve_offset);
                err |= preserve_sve_context(sve_ctx);
        }

        if (err == 0 && user->extra_offset) {
                char __user *sfp = (char __user *)user->sigframe;
                char __user *userp =
                        apply_user_offset(user, user->extra_offset);

                struct extra_context __user *extra;
                struct _aarch64_ctx __user *end;
                u64 extra_datap;
                u32 extra_size;

                extra = (struct extra_context __user *)userp;
                userp += EXTRA_CONTEXT_SIZE;

                end = (struct _aarch64_ctx __user *)userp;
                userp += TERMINATOR_SIZE;

                /*
                 * extra_datap is just written to the signal frame.
                 * The value gets cast back to a void __user *
                 * during sigreturn.
                 */
                extra_datap = (__force u64)userp;
                extra_size = sfp + round_up(user->size, 16) - userp;

                __put_user_error(EXTRA_MAGIC, &extra->head.magic, err);
                __put_user_error(EXTRA_CONTEXT_SIZE, &extra->head.size, err);
                __put_user_error(extra_datap, &extra->datap, err);
                __put_user_error(extra_size, &extra->size, err);

                /* Add the terminator */
                __put_user_error(0, &end->magic, err);
                __put_user_error(0, &end->size, err);
        }

        /* set the "end" magic */
        if (err == 0) {
                struct _aarch64_ctx __user *end =
                        apply_user_offset(user, user->end_offset);

                __put_user_error(0, &end->magic, err);
                __put_user_error(0, &end->size, err);
        }

        return err;
}

static int get_sigframe(struct rt_sigframe_user_layout *user,
                         struct ksignal *ksig, struct pt_regs *regs)
{
        unsigned long sp, sp_top;
        int err;

        init_user_layout(user);
        err = setup_sigframe_layout(user, false);
        if (err)
                return err;

        sp = sp_top = sigsp(regs->sp, ksig);

        sp = round_down(sp - sizeof(struct frame_record), 16);
        user->next_frame = (struct frame_record __user *)sp;

        sp = round_down(sp, 16) - sigframe_size(user);
        user->sigframe = (struct rt_sigframe __user *)sp;

        /*
         * Check that we can actually write to the signal frame.
         */
        if (!access_ok(user->sigframe, sp_top - sp))
                return -EFAULT;

        return 0;
}

static void setup_return(struct pt_regs *regs, struct k_sigaction *ka,
                         struct rt_sigframe_user_layout *user, int usig)
{
        __sigrestore_t sigtramp;

        regs->regs[0] = usig;
        regs->sp = (unsigned long)user->sigframe;
        regs->regs[29] = (unsigned long)&user->next_frame->fp;
        regs->pc = (unsigned long)ka->sa.sa_handler;

        if (ka->sa.sa_flags & SA_RESTORER)
                sigtramp = ka->sa.sa_restorer;
        else
                sigtramp = VDSO_SYMBOL(current->mm->context.vdso, sigtramp);

        regs->regs[30] = (unsigned long)sigtramp;
}

static int setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set,
                          struct pt_regs *regs)
{
        struct rt_sigframe_user_layout user;
        struct rt_sigframe __user *frame;
        int err = 0;

        fpsimd_signal_preserve_current_state();

        if (get_sigframe(&user, ksig, regs))
                return 1;

        frame = user.sigframe;

        __put_user_error(0, &frame->uc.uc_flags, err);
        __put_user_error(NULL, &frame->uc.uc_link, err);

        err |= __save_altstack(&frame->uc.uc_stack, regs->sp);
        err |= setup_sigframe(&user, regs, set);
        if (err == 0) {
                setup_return(regs, &ksig->ka, &user, usig);
                if (ksig->ka.sa.sa_flags & SA_SIGINFO) {
                        err |= copy_siginfo_to_user(&frame->info, &ksig->info);
                        regs->regs[1] = (unsigned long)&frame->info;
                        regs->regs[2] = (unsigned long)&frame->uc;
                }
        }

        return err;
}

static void setup_restart_syscall(struct pt_regs *regs)
{
        if (is_compat_task())
                compat_setup_restart_syscall(regs);
        else
                regs->regs[8] = __NR_restart_syscall;
}

/*
 * OK, we're invoking a handler
 */
static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
{
        struct task_struct *tsk = current;
        sigset_t *oldset = sigmask_to_save();
        int usig = ksig->sig;
        int ret;

        rseq_signal_deliver(ksig, regs);

        /*
         * Set up the stack frame
         */
        if (is_compat_task()) {
                if (ksig->ka.sa.sa_flags & SA_SIGINFO)
                        ret = compat_setup_rt_frame(usig, ksig, oldset, regs);
                else
                        ret = compat_setup_frame(usig, ksig, oldset, regs);
        } else {
                ret = setup_rt_frame(usig, ksig, oldset, regs);
        }

        /*
         * Check that the resulting registers are actually sane.
         */
        ret |= !valid_user_regs(&regs->user_regs, current);

        /*
         * Fast forward the stepping logic so we step into the signal
         * handler.
         */
        if (!ret)
                user_fastforward_single_step(tsk);

        signal_setup_done(ret, ksig, 0);
}

/*
 * Note that 'init' is a special process: it doesn't get signals it doesn't
 * want to handle. Thus you cannot kill init even with a SIGKILL even by
 * mistake.
 *
 * Note that we go through the signals twice: once to check the signals that
 * the kernel can handle, and then we build all the user-level signal handling
 * stack-frames in one go after that.
 */
static void do_signal(struct pt_regs *regs)
{
        unsigned long continue_addr = 0, restart_addr = 0;
        int retval = 0;
        struct ksignal ksig;
        bool syscall = in_syscall(regs);

        /*
         * If we were from a system call, check for system call restarting...
         */
        if (syscall) {
                continue_addr = regs->pc;
                restart_addr = continue_addr - (compat_thumb_mode(regs) ? 2 : 4);
                retval = regs->regs[0];

                /*
                 * Avoid additional syscall restarting via ret_to_user.
                 */
                forget_syscall(regs);

                /*
                 * Prepare for system call restart. We do this here so that a
                 * debugger will see the already changed PC.
                 */
                switch (retval) {
                case -ERESTARTNOHAND:
                case -ERESTARTSYS:
                case -ERESTARTNOINTR:
                case -ERESTART_RESTARTBLOCK:
                        regs->regs[0] = regs->orig_x0;
                        regs->pc = restart_addr;
                        break;
                }
        }

        /*
         * Get the signal to deliver. When running under ptrace, at this point
         * the debugger may change all of our registers.
         */
        if (get_signal(&ksig)) {
                /*
                 * Depending on the signal settings, we may need to revert the
                 * decision to restart the system call, but skip this if a
                 * debugger has chosen to restart at a different PC.
                 */
                if (regs->pc == restart_addr &&
                    (retval == -ERESTARTNOHAND ||
                     retval == -ERESTART_RESTARTBLOCK ||
                     (retval == -ERESTARTSYS &&
                      !(ksig.ka.sa.sa_flags & SA_RESTART)))) {
                        regs->regs[0] = -EINTR;
                        regs->pc = continue_addr;
                }

                handle_signal(&ksig, regs);
                return;
        }

        /*
         * Handle restarting a different system call. As above, if a debugger
         * has chosen to restart at a different PC, ignore the restart.
         */
        if (syscall && regs->pc == restart_addr) {
                if (retval == -ERESTART_RESTARTBLOCK)
                        setup_restart_syscall(regs);
                user_rewind_single_step(current);
        }

        restore_saved_sigmask();
}

asmlinkage void do_notify_resume(struct pt_regs *regs,
                                 unsigned long thread_flags)
{
        /*
         * The assembly code enters us with IRQs off, but it hasn't
         * informed the tracing code of that for efficiency reasons.
         * Update the trace code with the current status.
         */
        trace_hardirqs_off();

        do {
                /* Check valid user FS if needed */
                addr_limit_user_check();

                if (thread_flags & _TIF_NEED_RESCHED) {
                        /* Unmask Debug and SError for the next task */
                        local_daif_restore(DAIF_PROCCTX_NOIRQ);

                        schedule();
                } else {
                        local_daif_restore(DAIF_PROCCTX);

                        if (thread_flags & _TIF_UPROBE)
                                uprobe_notify_resume(regs);

                        if (thread_flags & _TIF_SIGPENDING)
                                do_signal(regs);

                        if (thread_flags & _TIF_NOTIFY_RESUME) {
                                clear_thread_flag(TIF_NOTIFY_RESUME);
                                tracehook_notify_resume(regs);
                                rseq_handle_notify_resume(NULL, regs);
                        }

                        if (thread_flags & _TIF_FOREIGN_FPSTATE)
                                fpsimd_restore_current_state();
                }

                local_daif_mask();
                thread_flags = READ_ONCE(current_thread_info()->flags);
        } while (thread_flags & _TIF_WORK_MASK);
}

unsigned long __ro_after_init signal_minsigstksz;

/*
 * Determine the stack space required for guaranteed signal devliery.
 * This function is used to populate AT_MINSIGSTKSZ at process startup.
 * cpufeatures setup is assumed to be complete.
 */
void __init minsigstksz_setup(void)
{
        struct rt_sigframe_user_layout user;

        init_user_layout(&user);

        /*
         * If this fails, SIGFRAME_MAXSZ needs to be enlarged.  It won't
         * be big enough, but it's our best guess:
         */
        if (WARN_ON(setup_sigframe_layout(&user, true)))
                return;

        signal_minsigstksz = sigframe_size(&user) +
                round_up(sizeof(struct frame_record), 16) +
                16; /* max alignment padding */
}